Demand on a high speed of an access network speed has been increased rapidly as well-known voice telephone and text oriented services have evolved to video and image oriented multimedia services due to a rapid expansion of Internet. Due to such a trend ease of information recognition, it is expected that newly emerging services to be developed in the future will be mostly video oriented multimedia services. Therefore, a next-generation access network is required to have a structure capable of effectively accommodating the video and image oriented multimedia services. Further, it is required to be able to provide a triple play service (TPS), where voice telephone services, data telecommunications services, and high-definition video services are integrated into one service, through one network infrastructure. A wavelength division multiplexed-passive optical network (WDM-PON) is recognized as an ultimate alternative as a method capable of providing protocols to be used for a TPS and a bandwidth with no substantial limit while independently of a transmission speed with subscribers. Generally, since telecommunication is made by using wavelengths which are different from one another depending on respective subscriber in a WDM-PON, it is necessarily required to embody low-cost optical transceiver modules and systems. In addition, the use of a colorless light source is also necessarily required so as for all the subscribers to use a same light source, in order to save installation and maintenance costs of an access network.
studies on a tunable laser have been proceeded in order to embody a colorless light source described above. As one example, an external cavity laser (ECL) may change a lasing wavelength by controlling temperature of a grating. Such an ECL is considered as one possible light source to be used for a WDM-PON, since it can be embodied at relatively low-costs compared with existing lasing lasers. Further, tunable lasers including an ECL described in detail above can be used as light sources, etc. of a WDM optical transmission system being used at a metro network or a backbone network as well as a WDM-PON and thus have a high possibility of application, since they are able to perform modulation at a high speed.
Meanwhile, in order to use the tunable laser described above as a light source of a WDM optical transmission system and a WDM-PON, it is required to match the lasing wavelength of the tunable laser with the transmission wavelength of a wavelength division multiplexer/de-multiplexer. As a specific method and a device for accomplishing such a purpose, Jung-Hyung Moon, et al., for example, suggested a device for controlling a lasing wavelength of a tunable laser published in March of 2009 in an article entitled “An Automatic Wavelength Control Method of a Tunable Laser for a WDM-PON”, IEEE Photon. Technol. Lett., vol. 21, no. 5, pp. 325-327. The device for controlling a lasing wavelength of a tunable laser suggested by Jung-Hyung Moon, et al. is directed to a method which transmits incoherent light outputted from a broadband light source (BLS) to a tunable laser, and matches the lasing wavelength of the tunable laser with the transmission wavelength of a wavelength division multiplexer/de-multiplexer by using an optical beating component generated between an optical signal outputted from the tunable laser and the incoherent light. However, an additional BLS is required, and an optical coupler, a reflector, for example, such as a mirror, and a photodiode are required to be used per each channel or each subscriber, in the method disclosed in the article as described above. Since the use of additional equipment causes to increase the costs of a WDM optical transmission system and a WDM-PON, a more cost-effective method is needed.
Besides, in a WDM optical transmission system and a WDM-PON, a method of controlling a lasing wavelength of a tunable laser manually or finding the lasing wavelength using a look-up table has been used in order to match the lasing wavelength of a tunable laser with the transmission wavelength of a wavelength division multiplexer/de-multiplexer. However, such a manual method or a method using a look-up table has a disadvantage that is difficult to embody cost-effectively, because it requires a lot of professional human resources and substantial time.
Accordingly, a new method capable of embodying a WDM optical transmission system and a WDM-PON cost-effectively by controlling a lasing wavelength of a tunable laser automatically.